1. Field of the Invention
The present invention relates to a plasma generating apparatus and a plasma processing apparatus provided with the same, and more particularly to a plasma generating apparatus used for plasma CVD, plasma etching and other plasma processing, and a plasma processing apparatus provided with the same. The plasma CVD is performed for depositing a film on a substrate in a process of producing various kinds of sensors provided with semiconductors and other devices utilizing semiconductors as well as solar cells and others. The plasma etching is performed, e.g., for etching a deposited film in accordance with a predetermined pattern so as to form interconnection patterns or the like. The plasma generating apparatus is also used for the plasma processing which is performed, e.g., for improving quality of a surface of a substrate with plasma.
2. Description of the Background Art
In general, plasma of a high density which is required in the plasma processing is generated by such a method that an excitation gas is changed into plasma by thermoelectrons emitted by heating a filament, and a processing gas is excited by ions in the plasma to form plasma.
An example of an apparatus used for such plasma processing will be described below in connection with a plasma processing apparatus shown in FIG. 2. This apparatus includes a plasma producing chamber 1 and a processing chamber 2 which are communicated with each other and are grounded.
A filament 3 forming a plasma source is disposed in the plasma producing chamber 1. The filament 3 is connected to a DC power supply 4. An ion leading electrode 5 is disposed under the filament 3. A DC power supply 6 is connected between the electrode 5 and a substrate holder 10 which will be described later. The plasma producing chamber 1 is connected to a gas supply 7 for an excitation gas via a piping. The gas supply 7 includes one or more gas sources 731, 732, . . . for excitation gases connected to pipings provided with mass-flow controllers 711, 712, . . . and valves 721, 722, . . . , respectively. Around the plasma producing chamber 1, there is disposed a ring-shaped solenoid magnet 8 for converging the generated ions toward the processing chamber 2.
The substrate holder 10 is disposed in the lower portion of the processing chamber 2, and is provided with a heater 10a for heating a substrate S2 mounted on the holder 10 to a processing temperature. When the substrate S2 is to be heated by radiant heat, the heater 10a is spaced from the holder 10. If required, a cooler may be used instead of the heater 10a.
The holder 10 is connected to an rf (radio-frequency) power supply 12 via a matching box 11, or is connected to a DC power supply 13 or 14. A selector switch 15 is operable to select the power supply 13 or 14. If the substrate S2 mounted on the holder 10 is electrically conductive, a DC voltage is applied from the DC power supply 13 or 14 to control the incident plasma for controlling the processing rate. If the substrate S2 is an electrical insulator, an rf voltage is applied by the rf power supply 12 to control the incident plasma for controlling the processing rate.
Above the holder 10, there is disposed a ring-shaped gas injection pipe 16, which is provided at its lower surface portion faced to the holder 10 with a large number of gas nozzles. The gas injection pipe 16 is connected to a gas supply 18 for a plasma processing gas via a gas introduction pipe 17. The gas supply 18 includes one or more gas sources 183a, 183b, . . . for the plasma processing gas via mass-flow controllers 181a, 181b, . . . and valves 182a, 182b, . . . , respectively. The excitation gas supply 7 and the plasma processing gas supply 18 are connected to the chambers 1 and 2 via different pipings for the following reason. If these gases were mixed together, particles forming dust are likely to be generated, and thus would contaminate the surface of the substrate S2 and interiors of the chambers 1 and 2. A ring-shaped solenoid magnet 9 is disposed along the outer peripheral wall of the processing chamber 2, and an exhausting device 19 is connected to the processing chamber 2. The solenoid magnet 9 is provided for converging ions toward the substrate S2 on the holder 10.
According to this plasma processing apparatus, the substrate S2 is held on the substrate holder 10, and then the exhausting device 19 is operated to set the chambers 1 and 2 to a predetermined degree of vacuum. Then, the excitation gas is introduced into the plasma producing chamber 1 from the gas supply 7, and the DC power is applied from the power supply 4 to the filament 3. Thereby, thermoelectrons are emitted from the heated filament 3, so that the plasma is generated from the introduced excitation gas. The ions in the plasma are accelerated and moved into the processing chamber 2 by the ion leading electrode 5, to which a voltage is applied from the DC power supply 6.
Meanwhile, the plasma processing gas is introduced to the vicinity of the substrate S2 via the gas introduction pipe 17 and the gas injection pipe 16 from the gas supply 18. The ions supplied from the plasma producing chamber 1 are converged toward the substrate S2 owing to the magnetic field formed by the solenoid magnet 9. The plasma processing gas introduced to the vicinity of the substrate 2 is excited by the ions to form the plasma, so that intended plasma processing is performed on the surface of the substrate S2. By this processing, etching is performed if the plasma processing gas is a gas for etching. If it is a gas for deposition, a film is deposited. If it is a gas for improving the quality of the surface, the quality of the substrate surface is improved.
In this plasma process, however, the filament 3 is liable to break if the pressure in the chambers 1 and 2 is high. Therefore, the pressure in the chambers to be maintained at a high degree of vacuum cannot be higher than 1.times.10.sup.-4 Torr. This increase a cost as compared with that for the plasma processing at a normal pressure. If the substrate to be processed is made of a material such as plastics which is likely to vaporize at a lower pressure, it is difficult to increase the degree of vacuum.
Even in the plasma processing at a high degree of vacuum of the pressure not higher than 1.times.10.sup.-4 Torr, if an inert gas or the like is used as a major gas of the excitation gas, and a gas containing an oxygen (O.sub.2) gas is additionally contained in the excitation gas for generating oxygen (O) plasma, the filament 3 breaks when the processing is performed for about ten hours in total even if a content of the oxygen gas is low and not higher than 10%.
The filament is generally made of metal having a high melting point such as tungsten (W). Similarly to the case where the oxygen gas is used as the excitation gas, if the excitation gas contains, for example, oxygen or halogen, metal of the filament forms oxide or halide and this compound vaporizes, so that the filament is consumed and a life-time thereof decreases. Further, the vaporized metal oxide or metal halide adheres, as impurity, onto the surface of the substrate and/or the interior of the vacuum container, and contaminates them.